1. Field of the Invention
This invention relates to melt-processible, moisture-curable ethylene copolymers which contain hydrolysable groups. The polymers are prepared by reacting a polymer containing glycidyl groups with a specified amino compound. They are useful, inter alia, as hot-melt adhesives and sealants, coatings, and as components of co-extruded film.
2. Description of Related Art
Crosslinked polymers have many desirable properties such as high heat resistance, good abrasion and cut resistance amongst many more. However, they can not be melt processed. Thermoplastic polymers, on the other hand, have the advantage of ready processibility in the melt. Thermoplastic polymers with a readily crosslinkable unit which may be crosslinked after thermoplastic processing may possess the advantages of both. The crosslinkable units may require additional substances or treatment to achieve effective crosslinking, and/or they may be subject to auto-crosslinking under various conditions such as temperatures higher than their thermoplastic processing temperatures.
A major difficulty with thermoplastic polymers which are potentially crosslinkable can be the prevention of crosslinking during their preparation. Even if this is avoided, a further difficulty can be prevention of even small amounts of crosslinking during the thermoplastic processing, since this leads to low melt flow and lack of control during processing. An alternative is a two-part system, where two polymers react together to crosslink. However, a one-part system has obvious advantages.
Crosslinking reactions during preparation and processing are thus undesirable. The desired crosslinking reaction is that which occurs AFTER thermoplastic processing. If this reaction requires addition of new substances, including a second polymer (i.e. two part systems), catalysts, or treatment other than thermal, such as radiation, to activate or react with the crosslinkable unit, the problem of crosslinking during melt (i.e thermoplastic) processing may not present itself. However, crosslinking systems which involve such substances or treatments are not always the most desirable, and there is a continuing search for thermoplastic crosslinkable polymers which are readily prepared without crosslinking during preparation, are highly melt stable during thermoplastic processing, but are subsequently very readily crosslinkable.
A well known readily crosslinkable unit which has been used in thermoplastic crosslinkable polymers is the silane unit because it can readily crosslink with simple moisture treatment. Such treatment has obvious advantages over radiation crosslinking or treatment with additional substances (other than water). While it is necessary to keep polymers containing such a unit free from moisture conditions which would cause crosslinking before and during thermoplastic processing, keeping polymers dry is a well established procedure. However, ready preparation of polymers containing a controlled level of silane groups where the resulting polymers are also thermally stable (and hence thermoplastically processible) has proved a problem. Often the reactions necessary to incorporate silane groups lead to other moieties which are thermally unstable, or which can themselves activate crosslinking of the silane or other groups.
Commercially, the only one-part, moisture curable hot-melt adhesives on the market are polyurethane based. These materials are currently `under the gun` however, due to residual isocyanates. In addition, as adhesives they often have poor `green` strength, often necessitating clamping, as well as poor thermal stability.
Ethylene copolymer based adhesives are in common use. However there are no commercial one-part curable ethylene copolymer based adhesives. Certain silane containing ethylene copolymer based curable materials, useful for adhesives have however been disclosed. U.S. Pat. No. 5,210,150 (Prejean) discloses one method of making fairly melt stable silane containing ethylene copolymer-based, moisture-curable polymers. Here, ethylene copolymers containing a carboxylic acid group are reacted, in the melt, with a stoichiometric amount of an epoxysilane, (a silane containing an epoxide group), the stoichiometric amount being critical in preventing thermal instability.
U.S. Pat. No. 3,408,420 (Wiggill) discloses the reaction used in Prejean, and other reactions where the polymer may contain a vinyl ester or acid chloride group, and is reacted, in solution, with a silane containing an epoxide or secondary amino or secondary alcohol group to produce the silane containing graft polymer.
While the silane containing polymers disclosed in U.S. Pat. No. 5,210,150 referred to above are adequate, still further improvements in preparative ease, melt stability and moisture cure-rate are desirable. There is thus a need for alternative methods of producing melt stable ethylene copolymer-based, thermoplastic silane containing crosslinkable materials, preferably using reactions in the melt.